Is Disciples purely turn-based, or can it be configured to play in real-time also?

Most definitely turn-based. There are 6 fields for units in each stack, some take up two and the leader takes up one, which leaves 3 fields free at the first. The last two are gained after leveling the leader up a little. And that's the battles.

Does the gold edition give the option of playing in a window?

No idea, though probably not.

1. Yes - Pure Turn-based.
2. No - Can't be run in a 'Windowed' mode. (Disciples 2 can be tho)

Really? The demo has a config file that seems to have a window option, but it crashes the demo. You have to open it in notepad and change the window option from 0 to 1.
Could someone with the gog version try it, please?

Well, I haven't tried it, but the configuration manager that comes with Disciples II Gold has an option to run the game in a window.

Look at the Configuration program.
You can obviously set it in Windowed mode, and it works for the most part, there is an annoying bug which won't end your turn after you pressed the End Turn button until you click outside of the window then once again select the window, but that takes about a second to do.
Also, some of the crashes reported in this thread are most likely due to the fact that for some reason when running the program windowed it will lock up if you're fiddling around with other programs at the same time. Boot the game up and give it a chance to properly load everything or else it might crash.
Windowed mode is pretty buggy.